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GM mosquito tricks get cleverer

September 2014
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Aedes aegypti mosquito. CC photo by Sanofi Pasteur on Flickr

Mosquitoes aren't human food. But humans are food for mosquitoes.

As mosquitoes feed off you, they inject saliva into you to keep their food (your blood) flowing out. During this, they can also transmit diseases such a malaria and dengue, and the latest thing in GM mozzies can also give you a dose of destructive DNA.

Natural mosquitoes are part of a serious health problem. GM mozzies could be much worse.

Realising that governments in mosquito-plagued areas would pay a lot of money to rid themselves of the problem, genetic engineers have been trying out some GM tricks to make the insects self-destruct.

The first tactic was to flood the area with waves of sterile GM males which are able to mate but whose offspring have a gene which makes them self-destruct (for unknown reasons) at the embryonic stage. By 'flood' we mean weekly releases of 10 million GM mosquitoes for every 50,000 inhabitants in the area. That's a lot of very expensive mozzies. And, because the GM trait dies out without being passed on, churning out replacements is good business.

The second tactic is even more clever.

GM male mosquitoes produce sperm cells in which the chromosome which would produce females is shredded. This means their mates can only produce male offspring. Since the 'shredder' gene is passed on to the next all-male generation, the tactic permanently distorts the male-female ratio, and the mozzie population should be wiped out entirely after a few generations. This isn't such good business because the GM males don't have to be re-released so often, but probably easier to sell to governments.

Business apart, there are serious concerns at every level possible regarding the long-term safety of GM mosquito releases.

At the environmental level, wholesale self-destructing mozzies create a gap which will be filled. Most likely the same type of mosquito will migrate back in from other areas, re-creating all the same problems as before. Or, other opportunistic insects will move in, possibly bringing with them another problem.

At the level of the mosquito, safety has been based on the assumption that only the males are GM. Since the males don't bite, the human body isn't going to be exposed to them or their novel DNA.

However, this assumption is wrong: a few percent of GM females 'leak' into the system during mass production of the sterile males. In the second clever GM trick, the novel DNA which generates an enzyme to shred the 'female' chromosome can instead insert itself into the damaged genome, with the potential to create GM (biting) female offspring.

The most dangerous problem lies at the molecular level.

All the transgenic mosquitoes have been created using 'jumping' gene sequences to get the artificial DNA into their genome: 'jumping' genes can, by their nature, jump back out and jump into any other genome if there's a bit of DNA there they recognise.

Jumping genes are known to cause widespread mutations and disruption of gene function. What pestilence might evolve from GM mozzies with destabilised genomes could be bad news.

The GM genes could jump from cells in the saliva of GM female mosquitoes into the human they are biting. And what happens then?

In the case of clever GM mozzie trick No.1, the unknown mode of action of the gene product has unknown dangers.

In the case of clever GM mozzie trick No.2, self-destruction is achieved using enzymes designed to recognise specific DNA sequences and shred them. In mosquitoes, the target DNA is specific to the mosquito 'female' chromosome. However, similar DNA sequences are present in all higher organisms, including humans. Outside of its intended mozzie context, the GM shredder-system could wreak genomic havoc.

Jumping genes with DNA shredder enzyme capability have been found to be very toxic to cells. This, plus their capacity to replicate and hop through a cell population has led to their investigation as a treatment for killing cancer cells: the uncontrolled GM mosquito version is more likely to kill healthy cells.

Finally, the question has to be asked, do GM mosquitoes achieve their aim at the level of the disease they're designed to control?

In one area of Brazil where trial releases of GM mosquitoes have been carried to control dengue, a decree of a state of emergency due to dengue has just been renewed. As planned, the mosquito population has been reportedly decimated by 80-100%, but the dengue plague is getting worse.

It must be a tribute to clever marketing that Brazil has become the first country to approve the commercial use of GM mosquitoes, without any evidence that this will actually control the disease. Indeed, it has emerged that one member of the Brazilian regulatory authority which approved the trial prepared a report warning that the GM mosquito releases could make dengue worse even if the insect population was reduced (see below).

Note on why reducing the mosquito population might not reduce the disease it transmits.

Reducing the numbers of mosquitoes does not necessarily reduce the incidence of disease because the number of mosquitoes needed to transmit the disease is low.

Further, a different species of mosquito which also transmits dengue can move into the area.

Complex immune responses to the four types of dengue virus mean that a partial reduction in mosquito numbers can reduce the useful cross-immunity to the different sterotypes and could increase the number of cases of the severe form of the disease (Dengue Haemorrhagic Fever) which is more likely to be fatal.

Success in reducing illness in young children can mean cases of Dengue are more serious and delayed.

Commercial interests are so busy selling the idea behind their product, that they haven't stopped to check up on whether it's fit for its purpose. And human safety checks are nowhere in sight.

There's another way to combat dengue. There is an alternative non-transgenic system based on a common symbiotic bacterium that can stop the dengue virus multiplying in the mosquito host, which effectively makes those transgenic mosquitoes obsolete. But there's no patent and not much profit there.

Meanwhile, the GM-insect industry, based largely in England, seems set to flourish unchecked.

Do you wish these GM problems on areas already burdened by serious disease? Tell the Westminster Government to put some of your taxes towards providing vulnerable people with a real solution to dengue.

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